Network of Star Formation: Fragmentation controlled by scale-dependent turbulent pressure and accretion onto the massive cores revealed in the Cygnus-X GMC complex

TL;DR

This study introduces a triangulation-based method to analyze molecular cloud structures, revealing how turbulence and accretion influence core formation and growth in the Cygnus-X complex.

Contribution

A novel triangulation approach is developed to systematically study core-environment interactions and the transition from fragmentation to accretion in molecular clouds.

Findings

Core separation scales with surface density as $\Sigma_{edge} \propto l_{core}^{-0.28}$

Low-mass cores form primarily through fragmentation, while massive cores grow via accretion.

Massive cores show evidence of gas depletion due to accretion from their surroundings.

Abstract

Molecular clouds have complex density structures produced by processes including turbulence and gravity. We propose a triangulation-based method to dissect the density structure of a molecular cloud and study the interactions between dense cores and their environments. In our {approach}, a Delaunay triangulation is constructed, which consists of edges connecting these cores. Starting from this construction, we study the physical connections between neighboring dense cores and the ambient environment in a systematic fashion. We apply our method to the Cygnus-X massive GMC complex and find that the core separation is related to the mean surface density by $\Sigma_{\rm edge} \propto l_{\rm core }^{-0.28 }$, which can be explained by {fragmentation controlled by a scale-dependent turbulent pressure (where the pressure is a function of scale, e.g. $p\sim l^{2/3}$)}. We also find that the masses of low-mass cores ($M_{\rm core} < 10\, M_{\odot}$) are determined by fragmentation, whereas massive cores ($M_{\rm core} > 10\, M_{\odot}$) grow mostly through accretion. The transition from fragmentation to accretion coincides with the transition from a log-normal core mass function (CMF) to a power-law CMF. By constructing surface density profiles measured along edges that connect neighboring cores, we find evidence that the massive cores have accreted a significant fraction of gas from their surroundings and thus depleted the gas reservoir. Our analysis reveals a picture where cores form through fragmentation controlled by scale-dependent turbulent pressure support, followed by accretion onto the massive cores, {and the method can be applied to different regions to achieve deeper understandings in the future.